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Publication Number: FHWA-SA-97-019
Date: January 1997
At WesTrack, the Federal Highway Administration's (FHWA) accelerated pavement testing facility in Nevada, four heavily-laden triple-trailer trucks go round and round the 2.9-km (1.8-mi) track at precisely 65 km/h (40 mph) for at least 15 hours per day, every day of the year. Driving those trucks would be a tedious job for even the best of drivers-and tedium can often lead to inattention, which can lead to accidents. Realizing this, the WesTrack project team set out to find a way to take the driver out of the truck. The result: a system that allows the trucks to be operated entirely autonomously-no driver sits behind the steering wheel.
Each truck cab is outfitted with two computers-one for controlling the truck's path and speed, and one for monitoring the condition of various truck components and systems. An antenna mounted on the front of the truck picks up signals from wires buried in the pavement; those wires also transmit information back to five computers located in the central control room adjacent to the track. One person in the control room oversees the computers and the operation of the four trucks.
Some 160 sensors measure conditions in each truck, ranging from the air pressure in an individual tire to the air temperature in the cab. If any measurement falls outside an allowable range, the computer automatically shuts down the entire system, bringing all four trucks to a halt.
"The autonomous vehicle system has eliminated the risk of using drivers in an extremely monotonous driving situation," says Colin Ashmore, program manager for the Nevada Automotive Test Center, which is the prime contractor on the project.
The trucks have traveled more than 400,000 vehicle-kilometers (250,000 vehicle-miles) to date, applying over 1.5 million equivalent single-axle loads (ESALs).* There's been only one, minor accident, which occurred during a test of the software that forces the trucks to "wander" in the lane, mimicking real-world conditions. One of the trucks missed a guidance signal from the wire in the pavement, which immediately triggered all four trucks to come to a stop. One truck stopped with its nose at the top of the banked curve at one end of the track. Shortly afterward, an air supply line in the truck's braking system failed. The problem was amplified by an incorrectly installed check valve, which caused the brakes to release, sending the truck rolling down the embankment along the track and into the fence surrounding the track.
The truck sustained only minor damage-namely, a cracked front fender and a broken guidance antenna. The damage was easily repaired, and the truck was back on the track less than 24 hours later.
WesTrack is the first test track to make use of driverless trucks. But it probably won't be the last. "Only one minor incident in more than nearly a half-million vehicle-kilometers clearly indicates that the driverless system is the way to go for these types of projects," says Terry Mitchell, FHWA's contract manager for the project.
* An ESAL is equivalent to an 80-KN (18,000-lb) load applied to the pavement by two sets of dual tires on a single axle.
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